Inhibition of microbial growth in aldonic acid and aldonate compositions



United States Patent ABSTRACT OF THE DISCLOSURE Highly concentratedsolutions of aldonic acids, aldonates or mixtures thereof, are inhibitedagainst microbial growth by the addition of acetic acid or propionicacid. The invention is especially useful with highly concentratedsolutions of gluconic acid and gluconates containing a total dissolvedsolids of 50% to 90% by weight.

This invention relates to the inhibition of microbial growth in aldonicacid and aldonate compositions, and

more particularly to the inhibition of microbial growth in aqueoussolutions of gluconic acid and aqueous solutions of gluconates orgluconates and gluconic acid.

Gluconic acid is usually made commercially from glucose either bychemical oxidation or by fermentation processes. The free acid isusually sold as a 50% by weight solution in water. It is also possibleto prepare aqueous solutions of various gluconates, such as, forexample, sodium gluconate, potassium gluconate and/or ammoniumgluconate, as well as aqueous solutions of such gluconates containinggluconic acid.

Aqueous solutions of gluconic acid and/or gluconates are subject tomicrobial growth and especially to mold growth caused by variousmicroorganisms. Despite prior efforts to prevent microbial growth ingluconic acid solutions, the commercial solutions heretofore availablehave left much to be desired. In most instances they exhibit mold growthwhen allowed to stand around after being exposed to the atmosphere.Inhibitory agents, such as the chlorinated phenols, have been added tosuch solutions in an attempt to prevent the growth of microorganisms butthe use of such agents is undesirable where the products are to beemployed in applications that are likely to cause food contamination.

One of the objects of the present invention is to provide new andimproved aldonic acid solutions and aldonic acid-aldonate solutionswhich are inhibited against microbial growth by the incorporationtherein of an inhibitory substance that is not a food contaminant.

Another object of the invention is to provide new and improved gluconicacid and gluconic acid-gluconate liquid products which are inhibitedagainst microbial growth by the incorporation therein of a substancethat is not a food contaminant.

Still a further object of the invention is to provide a new and improvedmethod for inhibiting solutions of aldonic acid, solutions of aldonates,and solutions of aldonic acids and aldonates against microbial growth.

A more specific object of the invention is to provide a new and improvedmethod for inhibiting aqueous solutions of gluconic acid, aqueoussolutions of gluconates, and aqueous solutions of gluconic acid and oneor more gluconates against microbial growth. Other objects will appearhereinafter.

In accordance with the invention it has been found that aqueoussolutions of aldonic acids, aqueous solutions of aldonates, and aqueoussolutions of an aldonic acid and ice at least one aldonate can beinhibited against microbial growth by incorporating therewith a fractionof a percent by weight of acetic acid and/ or propionic acid. Sinceneither of these substances in the amounts efiective for the purpose ofthe invention is considered to be a food contaminant, the invention isespecially advantageous in providing liquid products inhibited againstmicrobial growth which are capable of being used not only for manyindustrial purposes but also in the food industry.

The effective dosage of acetic acid or propionic acid for the purpose ofthe invention is subject to some variation depending upon theconcentration and pH of the particular solutions of aldonic acid,aldonate or aldonic acidaldonate which is to be inhibited. In general,the amounts required are lower at the lower pHs and at higherconcentrations. Normally the invention is especially useful incompositions containing an aldonic acid and having a pH within the rangeof 1 to 5.

Typical examples of compositions to which the invention is applicableare: (1) commercial gluconic acid solutions, e.g., a 50% by weightsolution of gluconic acid in water; (2) mixtures of gluconic acid andsodium glucomate in water having a dissolved solids content of 50% to byweight and a weight ratio of gluconic acid to gluconate within the rangeof 0.06:1 to 44:1 preferably 0.2:1 to 4: 1; and (3) an aqueous solutionof a gluconate, e.g., ammonium gluconate, sodium gluconate and/orpotassium gluconate. A 50% by weight solution of gluconic acid in waterhas a pH of 1.2. The presence of sodium gluconate in conjunction withthe gluconic acid increases the pH but in most cases the pH will notexceed 5 and willusually be within the range of 3 to 4. On the otherhand, an aqueous solution of 23.7% by weight ammonium gluconate in waterhas a pH of 6.2. The addition of acetic acid and/ or propionic acid willproduce a drop in pH to some extent, depending upon the type of solutionand the amount added. The advantages of the invention are especiallysignificant when the pH of the composition to be inhibited is below ordoes not exceed 7.

In order to demonstrate the eflectiveness of the invention a number ofcompositions comprising gluconic acid and/or gluconates were prepared.Various proportions of acetic acid or propionic acid were added to thesecompositions. Some of the compositions were inoculated withmicroorganisms recovered from gluconic acid, gluconic acid-sodiumgluconate or ammonium gluconate solutions. Others were exposed to airwithout inoculation. The results were observed in comparison with thesame compositions to which no acetic acid or propionic acid had beenadded.

Mixed Aspergillus niger, Penicillium sp., and Spicaria sp. mold growthrecovered from gluconic acid solutions and mixed Aspergillus niger andPenicillium sp. mold growth recovered from gluconic acid-sodiumgluconate and ammonium gluconate solutions were used for the preparationof the inoculum suspensions. The procedure followed in inoculating thesetests was to suspend a total of four square centimeters of mold growth,the source and mixtures as indicated below, in ml. of the same liquidcomposition being tested, blend the mixture in a Waring Blendor for 10seconds and then use the suspension to inoculate the respective testsolutions at a 1% rate.

Inoeulum (sq. cm.) Per 100 m1. Suspension Source of MicrobialContaminants A B Glueonic acid, sodium gluconate solutions 4 Gluconicacid solutions g CNN The results obtained are shown in the followingexamples in which (v./v.) means volume per total volume and (w./W.)means weight per total weight. In these TABLE IRA) Microbial GrowthAfter Indicated Days at 28 C. (Inoculated) examples the amount ofmicrobial growth is indicated Acid a is 12 21 3o 40 50 6O 70 84 98 m asincreasing from 1 to 3, the growth indicated by the numeral 2 beinggreater than that indicated by 1 and the 0 2 2 3 3 3 3 3 3 3 growthindicated by 3 being greater than that indicated Acetic Acid 0.001 0 3 v3 3 3 3 3 g g g by 2. No microbial growth is indicated by 0. Sodium glu-69 8 g g g g g g 3 3 3 3 conate equivalent means the total gluconic acidand glu- 0 0 2 8 1 1 1 1 g g g 2; 2 2 conate content, calculated assodium gluconate. 10 0 0 0 0 O 0 0 0 0 0 0 0.25 0 0 0 0 0 0 0 0 0 0 0EXAMPLE 1 0.5 0 0 0 0 0 0 0 0 0 0 0 1.0 0 0 0 0 0 0 0 0 0 0 0 Aceticac1d and propiomc acid were added in varying 2.0 0 0 0 0 0 0 0 0 0 0 0concentrations to a solution of gluconic ac1d and sod1um Propionic Adam(L001 0 3 3 3 3 3 3 3 3 3 3 gluconate in water containing 26.3% gluconicacid and 0.005 0 2 2 3 3 3 3 3 3 3 3 60.7% sodium gluconate equivalent(gluconic acid:so- 96% g 8 3 8 3 8 8 8 3 8 6 diurn gluconate rat1o=0.84)having a pH of 3.6. The 0.5 0 0 0 0 0 0 0 8 g 8 8 treated solutions werethen held at 28 C. and examined 2 8 8 8 8 8 3 8 0 0 0 o periodically formicrobial growth. As indicated by the x3 8 8 8 g g g 8 8 g 8 3 data inthe following Table I, the addition of acetic ac d 0 0 0 0 0 0 0 o 0 0 0and propionic ac1d in excess of 0.01% to the gluconic acid-sodiumgluconate liquid product prevented the de- EXAMPLE 3 velopment ofmicrobial growth. Acetic acid and propionic acid were added in varyingTABLE I concentrations to a gluconic ac1d-sodium gluconate liquidproduct containing 33.0% (W./W.) gluconic acid andMlcmblalgrowliggemdmted days 60.2% (w./W.) sodium gluconate equivalent(gluconic I Percent acid:sodium gluconate ratio=1.4) having a pH of 3.3.Am (h/V9 0 22 47 The treated solutions were prepared in duplicate, andAcetic Acid 0.00 0 3 3 3 3 one set was inoculated with a mixedsuspension of fungi 38% g 3 g recovered from contaminated gluconicacid-sodium glu- 0.48 0 o 0 0 0 conate liquid solutions. The treatedsolutions were held 0 0 0 0 0 at 28 C. and examined periodically formicrobial Propionic Acid-.. 0.00 0 3 g g 3 growth. As indicated by thedata in the following Tables :85 8 8 0 0 0 III and III(A), the additionof acetic acid in excess of 0.43 0 g 8 8 8 0.05% or the addition ofpropionic acid in excess of 0 0.025% to the gluconic acid-sodiumgluconate liquid product prevented the development of microbial growth.EXAMPLE 2 TABLE HI Acetlc a and PYOPIQmC ac1d adqed m varlfmg 4OMicrobial Growth After Indicated Weeks concentrations to a solution ofgluconic ac1d and sodium at 28 0. (not inoculated) gluconate in watercontaining 30.7% (w./w.) gluconic Acid ag f 0 2 3 4 5 6 7 8 9 10 12 acidand 59.7% (w./w.) sodium gluconate equivalent (gluconic acid:sodiumgluconate ratio-1.2) having a Control 0 1 2 2 2 2 2 2 2 2 2 pH of 3.45.The treated solutions were prepared in dupli- Acetic Acid 0.025 0 1 2 22 2 2 2 2 2 2 cate, and one set was inoculated with a mixed suspension22 8 g 6 5 g g g 2 g of fungi recovered from contaminated gluconicac1d-' 0.1 0 0 0 0 0 0 0 0 0 0 0 sodium gluconate liquid solutions. Thetreated solutlons g g g 8 g g g g g g 8 g were held at 28 C. andexamined periodically for micro- 0.3 0 0 0 0 0 0 0 0 0 0 0 bial growth.As indicated by the data in the following Sz g g g g 8 3 g g g g 3Tables II and II(A), the addition of acetic acid in excess P i A 0 0025o of 0.05% or the addition of propionic acid in excess of mp m {L005 0 33 3 3 3 8 8 3 8 8 0.01% to the gluconic acid-sodium gluconate liquidprod- 0.0075 0 0 0 0 0 0 0 0 0 0 0 1 th 0.01 0 0 0 0 0 0 0 0 0 0 0 notprevented the development of micro 1a grow (L025 0 0 0 0 0 o 0 0 0 0 00.05 0 0 0 0 0 0 0 0 0 0 0 0.075 0 0 0 0 0 0 0 0 0 0 0 TABLE II 0.1 0 00 0 0 0 0 0 0 0 0 0.2 0 0 0 0 0 0 0 0 0 0 0 Microbial Growth AfterIndicated Days P t at 23 0. (Not inoculated) TABLE III(A) ercen Acid(v./v.) 0 12 21 30 40 50 00 70 34 03 112 g gg g fi fgg gg ffi PercentC(mtml 1 1 2 2 2 2 Acid (v./v.) 0 2 3 4 5 0 7 3 0 10 12 AceticAcid..-.0.001 0 1 1 1 1 1 1 1 2 2 2 0 2 2 2 2 2 2 2 2 2 2 0.010111111122202222222222 0.02500000000000 02222222222 00500000000000 00000000000 0.10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.2500000000000 000000000000500000000000 00000000000 1.0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 2.0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Propiouic Acid.-. 0 001 0 1 1 2 2 2 2 2 2 2 2 0.005 0 0 1 1 1 1 1 1 1 12 Propionic Acid". 0.0025 0 2 2 2 2 2 2 2 2 2 2 0.010000000000070.00502222222222 0.025 0 0 0 0 0 0 0 0 0 0 0 0.0075 0 2 2 2 2 2 2 2 2 22 00500000000000 0.0102222222222 0.0100000000000 0.02500001111111 0.25 00 0 0 0 0 0 0 0 0 0 0.05 0 0 0 0 0 0 0 0 0 0 0 0.5 0 0 0 0 0 0 0 0 0 0 00.075 0 0 0 0 0 0 0 0 0 0 0 1.000000000000 0.100000000000 20000000000000.200000000000 5 EXAMPLE 4 Acetic acid and propionic acid were added invarying concentrations to a solution of gluconic acid and sodiumgluconate in water containing 35.4% (w./w.) gluconic and 60.8% (w./w.)sodium gluconate equivalent (gluconic acidzsodium gluconate ratio=1.65)having a pH of 3.25. The treated solutions were prepared in duplicate,and one set was inoculated with a mixed suspension of fungi recoveredfrom contaminated gluconic acid and gluconic acid-gluconate liquidsolutions. The treated solutions were held at 28 C. and examinedperiodically for microbial growth. As indicated by the data in thefollowing Tables IV and IV(A), the addition of acetic acid in excess of0.025% or the addition of propionic acid in excess of 0.01% to thegluconic acid-sodium gluconate liquid product prevented the developmentof microbial growth.

TABLE IV Microbial Growth after Indicated Weeks at 28 0. (Notinoculated) Percent Acid -l Control Acetic Acid Propionic Acid TABLEIV(A) Microbial Growth after Indicated Weeks at 28 C. (Inoculated)Percent Acid Control Acetic Acid Propionic Acid oocoooooc ooocoooo o QcOOoOOOrw cooooooo N OOQOOOOHN 00000000 to occoov-nmw ocococcoocooovmzcie ooocoooo N OOOOOHMNN: ococooczcw w ooooowrewrc Ooooooocm M qOQOcoHroN-vlo Ooooooooro m m EXAMPLE Acetic acid and propionic acid wereadded in varying concentrations to a solution of gluconic acid andsodium gluconate in water containing 31.6% (w./w.) gluconic acid and63.3% (w./w.) sodium gluconate equivalent (gluconic acidzsodiumgluconate ratio=1.12 having a pH of 3.3. The treated solutions wereprepared in duplicate, and one set was inoculated with a mixedsuspension of fungi recovered from contaminated gluconic acid andgluconic acid-gluconate liquid solutions. The treated solutions wereheld at 28 C. and examined periodically for microbial growth. Asindicated by the data in the following Tables V and V(A), the additionof acetic acid in excess of 0.075% or the addition of propionic acid inexcess of 0.01% to the gluconic acid-sodium gluconate liquid productprevented the development of microbial growth.

TABLE v Microbial Growth after Indicated Weeks at 28 0. (Not inoculated)Percent Acid (v./v.) 0 2 3 4 5 6 7 8 9 10 Control 0. 00 0 2 3 3 3 3 3 33 3 Acetic Acid 0. 025 0 2 2 2 2 2 2 2 2 2 0.05 0 0 0 I 1 l 1 1 1 10.075 0 0 0 0 0 0 0 0 0 0 0. 1 0 0 0 0 0 0 0 0 0 0 0. 15 0 0 0 0 0 0 0 00 0 0. 2 0 0 0 0 0 0 0 0 0 0 0.3 0 0 0 0 0 0 0 0 0 0 0. 4 0 0 0 0 0 0 00 0 l] 0. 5 0 0 0 0 0 0 0 0 0 0 Propionic Acid 0. 0025 0 2 2 2 2 2 2 2 22 0.005 0 2 2 2 2 2 2 2 2 2 0 0075 0 1 2 2 2 2 2 2 2 2 0.01 0 1 l 2 2 22 2 2 2 0. 025 0 0 0 0 0 0 0 0 0 0 0.05 0 0 0 0 0 0 0 0 0 0 0. 075 0 0 00 0 0 0 0 0 0 0. l 0 0 0 0 0 0 0 0 0 0 0. 2 0 0 0 0 0 0 0 0 0 0 TABLEV(A) Microbial Growth after Indicated Weeks at 28 C. (Inoculated)Percent Acid (v./v.) 0 2 3 4 5 6 7 8 9 10 Control 0. 00 0 2 2 2 2 2 2 2Acetic Acid 0.025 0 2 2 2 2 2 2 2 2 2 0. 05 0 2 2 2 2 2 2 2 2 2 0.075 00 1 1 2 2 2 2 2 2 0. 1 0 0 0 0 0 0 0 0 0 0 0. 15 0 0 0 0 0 0 0 0 0 0 0.2 0 0 0 0 0 0 0 0 0 0 0.3 0 0 0 0 0 0 0 0 0 0 0. 4 0 0 0 0 0 0 0 0 0 00. 5 0 0 0 0 0 0 0 0 0 0 Propiouic Acid 0.0025 0 2 2 2 2 2 2 2 2 2 0.0050 2 2 2 2 2 2 2 2 2 0. 0075 0 2 3 3 3 3 3 3 3 3 0.01 0 2 2 2 2 2 2 2 2 20. 025 0 0 0 0 0 0 0 0 0 0 0. 05 0 0 0 0 0 0 0 0 0 0 0. 075 0 0 0 0 0 00 0 0 0 0. l 0 0 0 0 0 0 0 0 0 0 0. 2 0 0 0 0 0 0 0 0 0 0 EXAMPLE 6Acetic acid and propionic acid were added in varying concentrations to asolution of gluconic acid and sodium gluconate in water containing 31.7%(w./w.) gluconic acid and 60.3% (W./w.) sodium gluconate equivalent(gluconic acid:sodium gluconate ratio=l.27) having a pH of 3.35. Thetreated solutions were prepared in duplicate, and one set was inoculatedwith a mixed suspension of fungi recovered from contaminated gluconicacidsodium gluconate liquid solutions. The treated solutions were heldat 28 C. and examined periodically for microbial growth. As indicated bythe data in the following Tables VI and VI(A), the addition of aceticacid in excess of 0.075% or the addition of propionic acid in excess of0.025% to the gluconic acid-sodium gluconate liquid product preventedthe development of microbial growth.

TABLE VI Microbial Growth after Indicated Weeks at 28 C (Not inoculated)Percent Acid Iv.)

c 9999;.9 UbhQJNOU- OOQOQOOOQ 000000000 Q o Propionic Acid 0.

OOOOQOCOO ocooooooo l- COQOOOOOH 00600000! N; OQOOQOOON OCQOOOOON gOOOOOOOQM QOQOOOOON N C7! OOQOQOOHN DOOOOOOON oooooov-uw QOOOOOOON NOoOOOCD-l-KO QQQQQQDON N CoCQOI-I-HM OOOOOOOON N 5 OoOOoI-l-HM OOOOOOQONN 8 TABLE X Microbial Growth after Indicated Weeks at 28 C. (AllSolutions Inocu- Sodium Glucolated) nate Equivalent,

Percent (w./w.) 2 3 4 5 6 7 sodium gluconate liquid product preventedthe development of microbial growth.

5 Acid, Percent (v./v.)

mmmwmm Control, 0.0

TABLE IX Microbial Growth after Indicated Weeks at 28 C. (Notinoculated) Percent Acid Control.. 0.00 0 0 1 Acetic acid, 0.15

Propionic acid, 0.075.-.."

mwo dooa 0 0 Acetic Acid Propionlc Acid.

taining 35.4% (w./w.) gluconic acid and 60.8% (w./w.) sodium gluconateequivalent (gluconic acid:sodium gluconate ratio=1.65) having a pH of3.25. A replicate control sample of 60% (w./w.) sodium gluconatesolution was also prepared without acetic acid. All solutions were m 2 m2 #6 6 MM 8 2 D mm mm 6 2 h mm 5 2 ma 2 Gm 4 )MS A ooz (b xm I WW 2 1 mto \J T mow o 0. MW P u n .1 O a m m 0 A C inoculated with a mixedsuspension of fungi recovered from contaminated gluconic acid andgluconic acid-gluconate liquid solutions. The treated solutions wereheld at 28 C. and examined periodically for microbial growth.

As indicated by the data in the following Table XI, 0.1% acetic acidprevented microbial growth at all gluconate concentrations.

Acetic Acid- TABLE XI Microbial Growth After Indicated Weeks at 28 C.(All Solutions Inocu- Sodium Glucolated) nate Equivalent,

Propionle Acid.

Percent (v./ v.) Percent (w./w.)

EXAMPLE 10 Acetic acid (0.15%) and propionic acid (0.075%) were added tosolutions containing the indicated sodium gluconate equivalentconcentrations. The latter solutions were prepared from solutions ofgluconic acid and s0- EXAMPLE l2 dium gluconate in water containing34.9% (W./W.) gluconic acid and 61.0% (w./w.) sodium gluconate equivlent(gluconic acidcsodiurn gluconate ratio=1.2) having Acme gold andpropionic i E added in varying a pH of 3.2. A replicate control set ofsodium gluconate Foucentratlons to a glucqmc 0 hqmd contamsolutions wasalso prepared without either organic acid. i glucomc acld water havmg 3PH of All solutions were inoculated with a mixed suspension whlch wasPurchased from d f & of fungi recovered from contaminated gluconic acidand The treaied solutlons.were F a m duphcate and.one gluconicacid-gluconate liquid solutions. The treated soset was Inoculated wlt.ha mlxed su.spens.lon of fungl lutions were held at 28 C, and examinedperiodically for coyered.from contammfltefi glucoplc and and glucomcmicrobial growth. As indicated by the data in the followaFId'SOdmmgluconate hquld solutloqs' The f f solu" ing Table X, 0.15% acetic acidprevented microbial 7O 9 held at and exammed Perlodlcany for growth onand 60% Sodium gluconate equivalent microbial growth. As lndicated bythe data in the followsolutions and markedly reduced microbial growth atthe Tables XII and the addition of C t a d lower gluconateconcentrations. Propionic acid (0.075%) in excess of 015% the additionof PFOPiOIIiC acid in prevented microbialgrowth at all gluconateconcentraexcess of 0.025% to the gluconic acid liquid product tigns.prevented the development of microbial growth.

TABLE XIV(A) Microbial Growth after Indicated Weeks at 28 C.(Inoculated) Percent (v./v.)

Acid

Control Acetic Acid Propionic Acid ooooooooo coooooooo c o omcewcewwweecrereeeecceemaee 60397939393950! OCAJCAIWWOOWDJW OJ lewmwceeaeoeeeeowceeeeawceww w wwmeawweeuw oeuweaeeeeeoeaee co m wceeeeawwwmwoweoeooaeaweew ee WOUWWNWWWOJ 69503935307030 )3 wozwcewceueeuoeeeeeowoowwce m m wweecceewmue: cwweaeawwww u so wwoaeeeowweeeeowwoawweewm ee EXAMPLE 15 A B C D E Solution, pH. 3.3 4 6 Sodiumgluconate equivalent, percent (w./w.). 37 37 37 37 37 Gluconic acid;percent (w.lw)- 22.0 10.2 1:9 Ratio gluconic acidzsodium gluconate.-1.75 0. 40 0.

A replicate control set of samples were also prepared without theaddition of acetic acid. All solutions were inoculated, with a mixedsuspension of fungi recovered from contaminated gluconic acid andgluconic acid-gluconate liquid solutions. The treated solutions wereheld at 28 C. and examined at the end of two weeks for microbial growth.As indicated by the data in the following Table XV, the addition ofacetic acid prevented microbial growth and the effective acetic acidconcentration was a function of the particular solution pH.

TABLE XV Acetic Acid, percent (v./v.)

P 99995 rapierooooorere oocoorere U1 ocean-tore Q c ol-uewre O OOHNNNN HFrom the foregoing examples it will be seen that the invention iseffective over a wide range of proportions and concentrations. Thus,Examples 1 to 9 cover aqueous solutions of gluconic acid and sodiumgluconate in various proportions within the range of 0.84 to 2.51(weight ratio of gluconic acid to sodium gluconate) at a dissolvedsolids concentration of 60% (w./w.) sodium gluconate equivalent.Examples 10 and 11 cover tests carried out with liquid productscontaining 5-85% sodium gluconate equivalent Examples 12 and 13 involvethe treatment of commercial gluconic acid solutions. Example 14 isdirected toward the treatment of an ammonium gluconate solution. Example15 shows the treatment of solutions of sodium gluconate as well as thosecontaining gluconic acid and sodium gluconate.

From these examples it is apparent that acetic acid and propionic acidare very effective in inhibiting microbial growth in aqueous solutionsof an aldonic acid and/or an aldonate, more particularly gluconic acidand gluconates (e.g., sodium gluconate, potassium gluconate and/orammonium gluconate) and mixtures thereof. Other aldonic acids andaldonates to which the invention is applicable are arabonic acid,mannonic acid, gulonic acid, galactonic acid and talonic acid, theirsalts, and mixtures of the acid and salts.

Many different substances have been employed heretofore in an effort toinhibit microbial growth in solutions of aldonic acids such as gluconicacid solutions. For the most part chlorinated phenols have beenrecommended and are said to be effective in inhibiting the growth ofmold in gluconic acid solutions. Calcium and sodium propionate are knownto afford protection against mold and rope in some foods such as bread.However, the use of acetic acid or propionic acid for this purpose hasnot been recommended. Nor has it been recognized heretofore that smallamounts of acetic acid or propionic acid would be effective inpreventing the growth of microorganisms in acidic media containingaldonic acids. Since aldonic acids such as gluconic acid are made byfermentation process it is difficult to avoid contamination by variousmicoorganisms which later grow and produce contaminating growths in theproduct. A particular advantage of the Present invention resides in thefact that the effective inhibitory substances, viz., acetic acid andpropionic acid, are permitted in foods. Another special advantage of theinvention is that the acetic acid and propionic acid are effectiveinhibitors of micorbial growth in low dosages in solutions of aldonicacids and/or aldonates when the dissolved solids content is at least 50%by weight or more.

For practical purposes the dosage of the inhibitory acetic acid orpropionic acid is usually within range of 0.1 to 1.% (v./v.) but, as theexamples show, dosages as low as 0.01% (v./v.) or even 0.005% (v./v.)are effective in certain solutions.

In other solutions, such as those of Example 15, higher dosages arerequired, particularly where the pH is above 5. Thus, sodium gluconatesolutions (37% w./w.) having a pH of 6 and of 7 required the use of 0.6%and 0.8% acetic acid (v./v.), respectively, in order to completelyprevent microbial growth over a period of two weeks. These quantitiesare so small that they do not normally affect the use of the resultantproducts in washing solutions or for other purposes. Hence, the productsare especially useful in all types of washing and cleaning solutions,e.g. bottle washing solutions containing caustic soda.

The invention is hereby claimed as follows:

1. A liquid composition consisting essentially of water and at least 50%by weight dissolved solids of a substance from the group consisting ofgluconic acid, a gluconate and mixtures of gluconic acid and at leastone gluconate, said composition being normally susceptible to microbialgrowth, and a microbial growth inhibiting amount of a substance from theclass consisting of acetic acid and propionic acid.

2. An aqueous at least 50% by weight gluconic acid solution containing afraction of one percent by weight of acetic acid suflicient to inhibitmicrobial growth in said solution.

3. An aqueous at least 50% by weight gluconic acid solution containing afraction of one percent by weight of propionic acid suflicient toinhibit microbial growth in said solution.

4. A liquid composition having a dissolved solids con tent of at least50% by weight and consisting essentially of a mixture of gluconic acidand gluconate in water, the weight ratio of said gluconic acid to saidgluconate being within the range of 0.06:1 to 44:1, and a microbialgrowth inhibiting amount of a substance from the class consisting ofacetic acid and propionic acid.

5. A liquid composition having a dissolved solids content of at least50% by weight and consisting essentially of a mixture of gluconic acidand sodium gluconate in water, said composition containing gluconic acidand 15 sodium gluconate in a weight ratio of at least 02:1 and beinginhibited against microbial growth by addition thereto of acetic acid ina microbial growth inhibiting amount which is at least 0.01% by volumeof acetic acid calculated on the volume of said composition.

'6. A liquid composition having a dissolved solids content of at least50% by weight and consisting essentially of a mixture of gluconic acidand sodium gluconate in water, said composition containing gluconic acidand sodium gluconate in a weight ratio of at least 0211 and beinginhibited against microbial growth by addition thereto of propionic acidin a microbial growth inhibiting amount which is at least 0.005% byvolume of propionic acid calculated on the volume of said composition.

7. A liquid composition having a dissolved solids content of 50% to 90%by weight and consisting essentially of a mixture of gluconic acid andat least one gluconate in water, said composition containing gluconicacid and said gluconate in a Weight ratio of 0.2:1 to 4:1 and beinginhibited against microbial growth by the addition thereto of amicrobial inhibiting amount of acetic acid which is a fraction of apercent by volume of acetic acid calculated on the volume of saidcomposition.

8. A liquid composition having a dissolved solids content of to byweight and consisting essentially of a mixture of gluconic acid and atleast one gluconate in water, said composition containing gluconic acidand said gluconate in a weight ratio of 0.2:1 to 4:1 and beinginhi'bited against microbial growth by the addition thereto of amicrobial inhibiting amount of propionic acid which is a fracton of apercent by volume of propionic acid calculated on the volume of saidcomposition.

Levine et al.: Journal of Bacteriology, v01. 39, 1940, pp. 499-515;pages 499, 512 and 513 relied on.

MAURICE W. GREENSTEIN, Primary Examiner US. Cl. X.R. 99-224- PO-105U(5/69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.5, 485, O0}

Dated December 9 1969 Inventor(5) Jack Ziffer et a1 It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 7, line 26', "gluconic" should read --(gluconic-;

line 31, "280" should read "28".

Column 15, line 6?, "equivalent" should read --equivalent.--.

Column 14, line 29, "micorbial" should read --microbial--.

SIGNED AND SEALED JUN 9 197g Attcst:

Edward M. Fletcher, It.

WEEK 1 :75am, JR.

Attesting ()ffi i Commissioner of Patents PO-IObU (5/69) UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,485,00} DatedDecember 9, 1969 Inventor-(5) Jack ZiffGI et a1 It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 7, line 26, "gluconic" should read --(gluconic--;

line 31, "280" should read "28".

Column 15, line 6?, "equivalent" should read --equiva1ent.--.

Column 14, line 29, "micorbial" should read --m1crobial--.

SIGNED AND SEALED JUN 9 1970 I E Anew .Flet lm-Jrwmrm'nrsum, m. offi rCommissioner of Patent! Attesting

